ios - CMTimeCompare 是如何工作的？

Question

CMTimeCompare 是如何工作的？Apple 似乎在他们的文档中遗漏了返回值。

https://developer.apple.com/library/mac/#documentation/CoreMedia/Reference/CMTime/Reference/reference.html

我假设如果时间相等，它返回零并返回正数或负数 1，基于哪个更大？

Answer 1

从CMTime.h：

返回两个 CMTime 的数值关系（-1 = 小于，1 = 大于，0 = 相等）。

如果 time1 小于 time2，则返回 -1。如果它们相等，则返回 0。如果 time1 大于 time2，则返回 1。

编辑：

请注意：

无效 CMTimes 被认为等于其他无效 CMTimes，并且大于任何其他 CMTime。正无穷被认为小于任何无效的 CMTime，等于自身，并且大于任何其他 CMTime。不确定的 CMTime 被认为小于任何无效 CMTime，小于正无穷大，等于自身，并且大于任何其他 CMTime。负无穷被认为等于它自己，并且小于任何其他 CMTime。

Answer 2

对于比 更容易阅读的替代方案，请CMTimeCompare()考虑使用CMTIME_COMPARE_INLINE 宏。例如

CMTIME_COMPARE_INLINE(time1, <=, time2)

如果 time1 <= time2 将返回 true

Answer 3

这是Swift 5一个非常简单的解释，使用AVPlayerItem和它的.currentTime()和.duration

let videoCurrentTime = playerItem.currentTime() // eg. the video is at the 30 sec point
let videoTotalDuration = playerItem.duration // eg. the video is 60 secs long in total

// 1. this will be false because if the videoCurrentTime is at 30 and it's being compared to the videoTotalDuration which is 60 then they are not equal.
if CMTimeCompare(videoCurrentTime, videoTotalDuration) == 0 { // 0 means equal

    print("do something")
    // the print statement will NOT run because this is NOT true
    // it is the same thing as saying: if videoCurrentTime == videoCurrentTime { do something }
}

// 2. this will be true because if the videoCurrentTime is at 30 and it's being compared to the videoTotalDuration which is 60 then they are not equal.
if CMTimeCompare(videoCurrentTime, videoTotalDuration) != 0 { // != 0 means not equal

    print("do something")
    // the print statement WILL run because it IS true
    // this is the same thing as saying: if videoCurrentTime != videoTotalDuration { do something }
}

// 3. this will be true because if the videoCurrentTime is at 30 and it's being compared to 0 then 30 is greater then 0
if CMTimeCompare(videoCurrentTime, .zero) == 1 { // 1 means greater than

    print("do something")
    // the print statement WILL run because it IS true
    // this is the same thing as saying: if videoCurrentTime > 0 { do something }
}

// 4. this will be true because if the videoCurrentTime is at 30 and it's being compared to the videoTotalDuration which is 60 then 30 is less than 60
if CMTimeCompare(videoCurrentTime, videoTotalDuration) == -1 { // -1 means less than

    print("do something")
    // the print statement WILL run because it IS true
    // this is the same thing as saying: if videoCurrentTime < videoTotalDuration { do something }
}